Contamination of groundwater, i.e., underground water, is a major problem affecting, for example, sources of drinking water. Many contaminants are known or potential threats to human health. Some contaminants were once widely used in industrial and commercial activities, and they entered the soil and/or groundwater through improper or illegal disposal practices. Some contaminants are present in sewage and/or process waste-water and must be remediated before they are discharged into the waterway system. At present, billions of dollars are spent each year to remediate process waste-water, sewage, wastes that are radioactive, contaminated groundwater aquifers, and soil containing harmful contaminants. Remediation methods include above-ground methods and in-ground methods.
U.S. Pat. No. 5,611,936 to Fernando et al. (Fernando) discloses an above-ground method in which trichlorethylene can be removed from groundwater by air-stripping followed by absorption of the trichlorethylene-containing air-stream onto activated carbon. Other above-ground methods disclosed by Fernando include the addition of hydrogen peroxide or ozone to an aqueous solution containing the halogenated organic compound followed by high intensity ultraviolet irradiation.
U.S. Pat. No. 5,990,373 to Klabunde discloses nanoscale metal oxides, such as MgO, CaO and Fe2O3, useful for adsorbing certain toxic chemical compounds from, e.g., a liquid phase. However, U.S. Pat. No. 5,990,373 does not disclose or suggest a metal element, either alone or in combination with a metal oxide, useful for removing contaminants from a liquid phase.
Methods for removing contaminants from an aqueous stream with elemental metals are known. For example, U.S. patent application Ser. No. 2003/0039857 A1 discloses that water containing chlorinated hydrocarbons (CHs) can be treated by passing the contaminated water though a column of granular iron. The publication discloses that the CHs are transformed into benign compounds such as hydrocarbons, chloride and water. U.S. patent application Ser. No. 2003/0039857 A1 further discloses that the granulated iron can be for used in-ground remediation. This reference discloses that a porous “wall” of the granulated iron must, disadvantageously, be placed into the path of a contaminated groundwater plume containing a chlorinated hydrocarbon.
Other in-ground methods describe groundwater treatment done by, e.g., injecting a suitable agent into the groundwater through a bore hole. The remediation agent can either transform the target compound into a benign species, as discussed above, or render it insoluble. For example, an elemental metal can be used to remove a metal salt (or metalloid) contaminant from water by reducing the metal salt (or metalloid) with the elemental metal to form an insoluble species.
Fernando discloses that a bimetallic system of iron and 9% palladium can be used to reductively dechlorinate hydrocarbon solvents. However, the relatively high cost of the raw material palladium makes such a system unattractive for in-ground remediation, where the palladium cannot be recovered.
U.S. patent application Publication No. 2002/0151602 discloses nanoscale metallic and bimetallic colloid particles, defined by that publication as ranging from 1 to 999 nanometers in size, allegedly useful for dechlorinating hydrocarbon solvents and treating soluble metals and metalloids present in subsurface soil. The publication alleges that the use of colloidal particles increases the reactivity of the particles and allows for adjective colloidal transport. However, the reference does not disclose a supported elemental metal.
U.S. patent application Publication No. 2003/0039857 A1 discloses nanoscale metal and bimetallic particles allegedly useful for treating groundwater containing chlorinated contaminants. The nanoscale metal particles are formed by adding an aqueous sodium borohydride solution dropwise to an aqueous ferric chloride solution while stirring. The publication also discloses that the bimetallic particles may be supported on activated carbon, zeolite or silica. However, the reference does not disclose a particle where the reductant elemental metal is supported.
U.S. Pat. No. 6,045,925 to Klabunde et al. discloses a composite particle containing an elemental metallic core and a shell. However, the patent does not disclose a composite particle with elemental metallic shell and a core which is not an elemental metal, nor does it disclose the use of the composite material for removing contaminants from groundwater.